JERUSALEM, Nov. 28 — In coordinated assaults on Israelis in the Kenyan city of Mombasa today, terrorists fired shoulder-launched missiles at a crowded Israeli passenger jet, missing their target, minutes before three suicide bombers drove up to the doors of an Israeli-owned hotel and detonated their explosives.

The bombers killed themselves and 12 other people — most of them Kenyans — and wounded dozens more with a blast that, in a chaos of black smoke, screams and burning thatch, gutted the Paradise Hotel and incinerated some bodies beyond recognition.

Israeli and Kenyan officials said that though there were competing claims of responsibility, Al Qaeda was possibly behind the attacks.

The Bush administration said, however, that it might be premature to blame Al Qaeda.

Hours after the attacks in Kenya, in a separate suicidal assault inside Israel, terrorists tied to Yasir Arafat's Fatah faction turned guns and grenades on Israelis as they went to the polls to choose the leader of the dominant right-wing party, the Likud. At least six Israelis were killed in that incident, in the town of Beit Shean in the northern Jordan Valley.

As his citizens came under attack abroad and at home on a day of spiraling violence, Ariel Sharon, the incumbent prime minister, declared tonight that terrorists did not "look for reasons to kill Jews; their aim is to kill young and old, women and children, only because they are Jews."

Early returns indicated that Mr. Sharon won the Likud primary by a wide margin, defeating Benjamin Netanyahu, the Israeli foreign minister. With this victory, Mr. Sharon also won a mandate from his party to achieve the elusive peace and security he promised when he first ran two years ago.

Mr. Sharon charged Israel's spy agency, the Mossad, with responsibility for tracking down those behind the attacks in Mombasa. If Al Qaeda was responsible, it would be the first time the group targeted Israelis since the Sept. 11, 2002, terrorist attacks on the United States, although its leader, Osama Bin Laden, has sought to rally Arabs to his banner by inveighing against Israel.

The attacks raised the prospect that Israel might take a higher-profile role in the pursuit of fundamentalist Islamic terrorists worldwide, a change that security analysts said could alarm Arab states and complicate the Bush administration's plans for a possible war on Iraq.

As in the attack on a Bali nightclub last month that killed more than 180 people, most of them tourists, the twinned assaults in Kenya took place in a seaside resort town known more for its thriving tourist trade than for any radical politics.

But United States has been concerned about continued Al Qaeda activity in the region. In nearly simultaneous attacks on Aug. 7, 1998. on the American embassies in Nairobi, Kenya's capital, and in neighboring Tanzania, 224 people, including 12 Americans, were killed. Those bombings were attributed to Al Qaeda, and since 1998 the United States has given Kenya $3.1 million for antiterrorist training, a State Department official said.

Just on Nov. 12, the United States provided Kenya with $750,000 to improve airport security.

Mombasa is a popular destination for Israeli tourists, and those attacked today — both aboard the plane and in the Paradise Hotel — were on package tours set up by an Israeli tourist agency that runs weekly flights there. Many of the vacationers had taken their children on a vacation during Hanukkah. With a kosher restaurant and a synagogue, whose torah scrolls were rescued from the blaze today, the Paradise Hotel was particularly popular with Israeli tourists.

A senior official with the protection and security division of Israel's Shin Bet security agency said the attack was carefully planned and executed.

"We're looking at a very planned, organized attack against Israelis in Mombasa," the official said. "They were looking for Israelis to kill. If the incident succeeded, it would have resulted in the deaths of over three-to-four-hundred Israelis."

The Israeli government said three of its citizens, including two boys, were killed in the bombing at the hotel. Witnesses said most of those killed in the blast were members of a youthful Kenyan dance troupe that greeted the Israelis when they arrived at the Paradise. "They were singing and dancing with drums," said Kelly Hartog, a survivor of the attack. "They were kids, they were young girls."

Witnesses at the scene provided conflicting accounts of the bomb attack. Some said the bombers' sport utility vehicle, which was green, tucked in behind a bus carrying Israeli tourists to pass a barrier at the hotel's entrance. Others said the vehicle simply crashed through barrier.

Ms. Hartog, an editor at The Jerusalem Post, said her group had left the bus after their overnight flight and entered the hotel's dining room for breakfast when they heard a tremendous blast and felt the hotel tremble. "For a split second there was a complete silence, but then we started seeing the debris from the thatch roof," she said in a telephone interview. "And then people started screaming."

Ms. Hartog said she and others went to the aid of the wounded, including children, searching for drinking water and using makeshift stretchers to carry them to a boathouse, out of the blazing sun.

Israelis who had hoped to escape the pressures of life here found themselves engulfed by the familiar horrors of a suicide attack.

"It was like being back home, it really was," Ms. Hartog said. "It's the same pictures. And in one of these surreal things, when we got to the hotel here and saw CNN, it could have been a downtown street in Jerusalem."

The bombers' sport utility vehicle was obliterated in the attack, witnesses said. The bus that carried the tourists was scorched to a skeletal wreck.

The Israeli government dispatched at least four planes to Kenya today to bring home the dead, the wounded and the survivors and to carry investigators to the scene.

The senior Israeli intelligence official said the attack on the Israeli passenger plane occurred at about 7:30 a.m. Kenyan time, roughly 20 minutes before the hotel bombing and 15 miles away. He said that two missiles were launched at the plane, and that Israeli security agents at the scene recovered two spent canisters from what were probably SA-7 "Strela" missiles, a 30-year-old shoulder-launched, surface-to-air missile of Soviet manufacture.

President Bush was told of the attacks this morning during his daily intelligence briefing at his ranch in Crawford, Tex., where he is spending the Thanksgiving holiday, and he spoke with his national security adviser, Condoleezza Rice.

"We deplore this violence, and the president offers his condolences to the victims and their families," Gordon Johndroe, a White House spokesman, said. "We've offered assistance to the governments of Israel and Kenya as they pursue the investigation of these attacks."

Mr. Johndroe said it was too early to know whether Al Qaeda was behind the attacks. "It's premature at this time to either rule in or out whether Al Qaeda was involved or not."